Electrical coil formed from multilayer strip conductor



1960 J. STALEY ETAL 2,949,593

ELECTRICAL COIL FORMED FROM MULTI-LAYER STRIP CONDUCTOR Filed my 9, 1957 SIT-Z111: Z: 3 a

INVENTORS JOHN STALEY THOMAS E. LEWIS 5 975 BY X,

ATTORNEYS United States Patent ELECTRICAL COIL FORMED FROM MULTI- LAYER STRIP CONDUCTOR John Stale'y andv Thomas E. Lewis, Louisville, Ky., as-

signors to Reynolds MetalsCompany, Richmond, Va., 7 a corporation of Delaware Filed May 9, 1957, Ser. No. 658,045 3 Claims. (Cl. 336186 a winding including a multi-layer strip conductor having insulated and uninsulated electrically conductive components adapted to be wound to provide an insulated coil and with the several components of the conductor being 1 physically separate from each other. It is well adapted to use in heavy duty coils, as in large size transformers wherein relatively thick conductors insulated by an inorganic coating and capable of operating at high temperatures are employed.

The advantages of an inorganic anodized film on a strip conductor, such as aluminum oxide on aluminum foil, over other types of applied insulation, are well known. In general, such anodic coatings not only give more permanent insulation, but also permit operation of the electrical equipment at higher temperatures and provide adequate insulation with a minimum of insulation thickness.

By means of the methods of edge treatment of such strip conductors, as disclosed in the co-pending application for US. Letters Patent, Serial No. 487,457, filed February 9, 1955. of which we are two of the three inventors thereof, such slitted strip conductors may now be provided with an anodically deposited insulation which affords uniform insulating ability and such insulation may be placed not only on both edges but, as desired, upon one or both sides of the conductor. As is known, however, even when the strip conductor is provided with the uniform inorganic insulation, the appreciable cost of that insulation and its inherent tendency to crack when bent upon a small radius are still present and may constitute disadvantages. It is these and similar limitations of the electrical conductor art which our invention is intended to overcome.

An object of our invention is to provide an improved multi-layer strip conductor having insulated and uninsulated electrically conductive components.

Another object is to provide an improved insulated electrical coil having a winding comprising a multi-layer strip conductor with insulated and uninsulated electrically conductive components.

. Another object is to provide an improved multi-layer strip conductor characterized by its mechanical flexibility.

A further object is to provide an improved multi-layer strip conductor with a relatively small insulated surface in proportion to its total cross section.

A further object is to provide an improved heavy duty anodically insulated electrical coil adapted to be wound with relatively small mechanical force and to conform readily to a predetermined shape of coil.

Other objects and advantages will become apparent as the description proceeds and when considered in conjunction with the accompanying drawings in which 2,949,593 Patented Aug. 16, 1960 Figure 1 is a perspective view of one form of coil embodying the invention and having a single electrical circuit therethrough;

Figure 2 is an illustration of the inner turn of the coil winding taken along line 2-2 of Figure 1;

Figure 2A is an illustration of the inner turn of a modified form of winding for heavy duty usage in a coil such as shown in Figure 1;

Figure 3 is a perspective view of a second form of coil embodying the invention and having two electrical circuits therethrough;

Figure 4 is an illustration of the inner turn of the coil winding taken along line 4-4 of Figure 3;

Figure 4A is an illustration of the inner turn of a modified form of winding for heavy duty usage in a coil such as shown in Figure 3;

Figure 5 is a perspective view of a third form of coil embodying the invention and having three electrical circuits therethrough;

Figure 6, is an illustration of the inner turn of the coil winding taken along line 6-6 of Figure 5; and

Figure 6A is an illustration of the inner turn of a modified form of winding for heavy duty usage in a coil such as shown in Figure 5.

In carrying out our invention we subdivide the strip conductor into physically separate insulated and uninsulated electrically conductive components which are so related that when wound into coil form the adjacent turns of that coil are insulated from each other. We have found that the ability of an anodically insulated strip conductor to bend about a coil forming mandrel or the like, without damage to the insulation, is in general inversely proportional to the thickness of that conductor. In contrast, an uninsulated conductor portion of the same material and of comparable or much greater thicknesses may be freely bent about the same mandrel without difficulty. By employing as the insulated component a thin conductor strip having its edges and at least one side covered by an anodic insulation placed thereon following a suitable edge treating operation (as disclosed by the above patent application) and by employing as the uninsulated component any desired number of bare strip conductors of any desired thicknesses, we provide a composite strip conductor which achieves the objectives set forth above. One additional advantage of our invention is that the eddy current losses are lower than by using conventional techniques. It will be noted particularly that each of the strip layers so employed is separate from the other layers and all are simultaneously bent into shape during the coil forming operation. The composite strip conductor is referred to herein as a multi-layer strip conductor.

Referring now to Figs. 1 and 2 showing an elementary form of our invention, a simple coil indicated at- 10 may comprise a winding having a number of turns and forming a single electrical circuit. Terminal leads 11 and 12 extend laterally from the winding.

As shown in Fig. 2, the innermost turn of the multilayer strip conductor includes a thin metal strip 13 which may consist of aluminum foil for example, having a width greatly in excess of its thickness. The strip 13 serves essentially as a mounting means for the coil insulation although it also contributes to the electrical conductivity of the winding. The strip 13 may comprise aluminum foil or sheet having a thickness in the range of 0.00017 to 0.060 inch or higher and on a first side thereof is covered with an anodic coating of aluminum oxide 14 have a thickness of about 0.0001 to 0.001 inch. The rounded lateral edges of strip 13, having previously been subjected to one of the aforementioned edge treating operations, also are covered with the same anodic coating which preferably extends around those edges and terminates on the second side of the strip along parallel lines disposed inboard of these edges at a distance equal to about 2-3 times the thickness of the strip 13. As will thus be seen, a substantial saving in the cost of depositing the anodic insulation is gained without adversely affecting the use of the coil, since the entire strip 13 need not be insulated. By reason of the flexibility due to its small thickness, the strip 13 may be bent upon the coil forming mandrel without damage to the inorganic insulation 14. In order to provide the necessary electrical conductivity for the coil when using the flexible thin strip 13, another strip 15 which may comprise uninsulated aluminum foil of greater thickness and of less width is disposed in contact with the second side of strip 13 and is bent simultaneously therewith in the forming of coil 10. The strips 13 and 15 are physically separate although in frictional contact with each other. Since no insulation is present between the juxtaposed surfaces found at the second side of strip 13 and the first side of strip 15, these strips form a single electricalcircuit through the coil and are jointly attached to the leadsll and 12, at the respective ends thereof. It can be appreciated that strip 13 may have insulation applied to both sides and still be in electrical contact with uninsulated strip 15 by virtue of the ends of the two strips being physically and electrically united to the same terminations 11 and 12. On the inner or second side 16 of the innermost turn of the winding, as

seen in Fig. 2, a suitable separate insulating layer of materialindicated in dotted lines at 17 normally is interposed between that side and the surface of the electrical device upon which the coil may be used. However, in some cases, it is desirable to leave this inner or second side uncovered so that it may come into direct electrical contact with an electrical conducting member onto which it is mounted. It will be understod that Fig. 2 illustrates only a single .turn for simplicity and that in the adjacent turn the uninsulated second side 16 will lie in contact with insulated first side 14 of the first turn and thatthis relation continues throughout the remainder of the coil. We prefer to employ strip 16 with a width less than the width of strip 13 so as to minimize the possibility ofarcing between adjacent turns. 'However, if desired, the strips 13 and 16 maybe of equal width or strip 16 may 7 be even of greater width and supplementary insulation may be used over the edges of those strips when the coil is formed. As used herein, the terms uninsulated component" and uninsulated layer are intended to apply to strip 16 and similar components of the strip conductor when its sides are uninsulated regardless of whether its edges may have such supplementary insulation. I

In heavy duty usage for this form of coil wherein 'a substantial cross section of conductor is required, the multi-layer strip conductor mayinclude a large number of uninsulated strips all comprising a single electrical circuit through the coil but capable of being readily wound as a unit. As shown in Fig. 2A, the multi-layer conductor may include not only the thin strip 13 insulated at 14 and the adjacent uninsulated strip 15 but also other uninsulated and physically separate strips 18 and 19, as well as others, if so desired. As will be apparent, by subdividing the required conductor cross section into a plurality of separate strips, not only is it possible to bend the anodized portion without damage thereto, but also the mechanical force required to bend the uninsulated portion is reduced and the separate strips or layers at the same time permanently conform more readily to the formationdictated by the winding mandrel. Of special significance, the amount of surface of the composite conductor covered by the anodic coating, when compared to the total cross section of the composite conductor, is relatively small and this factor is most noticeable in heavy duty forms of coils wherein an integrally formed strip: conductor would necessarily be thick and subjected tov insulation damage during the coil formation. t

Referring now to Figs. 3 and 4, a form of coil is shown in which two circuits may be established therethrough.

Coil 20 is provided with duplicate terminal leads 21, 22 and 23, 24 at the ends of the multi-layer strip conductor. This conductor, as shown in Fig. 4, includes as its insulated component a thin strip of metal 25 completely covered with an anodically deposited insulating coating 26, such as aluminum oxide. At its ends the strip 25 is connected to terminals 22 and 24, thus forming an insulated electrical circuit through the coil. As its uninsulated component, the conductor includes at least one separate strip 27 whose sides are uninsulated and one side 28 of which is adapted to contact the insulation 26 of strip 25 on one of the sides of that insulated strip and the other side 29 of which is adapted to contact the insulation 26 of strip 25 on the other side of that insulated strip in the wound arrangement of the conductor. As in the form of coil shown in Fig. 1, a separate insulating member 30 may be provided on the innermost section of the inner turn of the coil. At its ends the strip 27 is connected to terminals 21 and 23 thus forming a second electrical circuit through the coil, which separate circuit is insulated by reason of the relation of the uninsulated component of the strip conductor with respect to the insulated component thereof. As in the case of the coil in Fig. 1, the thin, anodically insulated strip 25 may be bent without damage to its insulation, but in this modification, the 'ratio of the insulated surface of the composite strip conductor to its total cross section is greater and thus a more expensive conductor is required. However, in usages wherein two circuits through the coil are needed, the expense of anodizing the uninsulated layer is avoided.

For heavy duty usages of coils having two circuits therethrough, a modified form, as shown in Fig. 4A, may be used. The strip 25 with its insulation 26 forms the insulated component of the multi-layer conductor, but strip 27 with its bare sides 28 and 29 forms only a portion; of the uninsulated component. Depending upon the metal employed and the total cross sections required,

additional uninsulated strips, such as shown at 31 and 32,

are used. It will'be understood that in this modified form of coil, strip 25 is connected to terminals 22 and 24 to form one circuit and that strips 27 31 and 32 are jointly connected to terminals 21 and 23 to form the second circuit.

In certain cases more than two circuits through the same coil may be required and in Fig. 5 a coil is shown embodying our invention and in which three circuits are used. It will be understod that the number of circuits may be multiplied indefinitely in coils of this type without departing from the invention, but, for brevity, only three variations of coils are described herein.

Referring to Figs. 5 and 6, coil 40 is provided with triplicate terminal leads, 41, 42, 43, and 44, 45, 46 at the on the innermost section of the inner turn of the coil.

ends of multi-layer conductor. As seen in Fig. 6, this conductor includes as its insulated component two spaced thin strips ofsuitably insulated metal 47 and 48. Strip 47 may be completely covered with an anodically deposited insulating coating 49 in which event strip 48 is covered with the coating only on the confronting side 50. However, if desired, the strip 48 can be completely covered, in which event, the other strip 47, is covered only on the side confronting the strip 48. At its ends the strip 47 may be connected to terminals 41 and 44 to form one circuit and the strip 48 at its ends may be connected to terminals 43 and 46 to form a second circuit.

As its uninsulated component, the conductor includes at least one separate strip 51 whose sides are uninsulated, one side 52 being in contact with the insulation 49 of strip 47 and the other side-53 being in contact with the insulation 50 of strip 48. As in the case of the coils of Figs. 1 and 3, a separate insulating member 54 may be provided At its ends the strip 51 is connected to terminals 42 and 45 thus forming a third circuit through the coil.

For heavy duty usage of coils having three circuits, at modified'form, as shown in Fig. 6A, may be used. The

strip 47 with its insuating 49 forms the first circuit. The second circuit is formed by strip 48 and one or more uninsulated strips 55, 56 in contact with the uninsulated side of strip 48 Between the spaces confronting insulated sides 49 and 50 of the insulated component of the conductor, uninsulated strip 51 and one or more similar strips 57, 58 are disposed in contact with each other. -It will be understood that in this modified form of coil strip 47 and strips 55,. 56 are jointly connected to terminals 43 and and strips 51 57, 58 are jointly connected to terminals 42 and 45, thus to form three separate circuits through the same coil.

It will be appreciated that in each of the figures depicting the several forms of coil embodying our invention, the respective strips or layers of the conductor are not drawn to scale. In general, the thickness of the insulated component or components of the composite multi-layer strip conductor is appreciably less than the thickness of the uninsulated component or components and in the preferred forms of coils the 'total cross section of all insulated components is less than the total cross section of all of the uninsulated components. The thin insulated component in all cases is flexible and may be bent into the desired coil shape without damage to the insulation.

We prefer to employ for all strips analuminum foil or sheet with rounded edges although if desired the rounded edge strips may be used only for the insulated components of the multi-layer strip. Moreover, in its broader aspects, the invention may be carried out with other insulation material or with other electrically conductive materials than aluminum, such as copper, or may be employed with some layers of the conductor formed of aluminum and other layers formed of copper.

Therefore, while we have shown particular embodiments of our invention, it will be understood of course, that we do not wish to be limited thereto, since many modifications may be made; and we therefore contemplate, by the appended claims, to cover any such modifications as fall within the true spirit and scope of our invention. I

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical coil construction including a multilayer flexible strip conductor wound in turn layer form, said conductor comprising a first layer consisting of a single aluminum strip having first and second sides and rounded edges, and a second metallic layer having uninsulated first and second sides, said layers being substantially coterminous and being arranged in side-by-side contact with each other, each of said layers being physically separate from each other and readily bendable around a forming mandrel, said first layer having an aluminum oxide insulation covering said first side thereof and establishing an insulating relation with respect to the second side of said second layer in the next succeeding turn of said coil and being uninsulated on at least a portion of the second side thereof for uninsulated contact I with the first side of said second layer, and terminals for said coil attached at at least one of said layers at the ends thereof and serving to connect said layers in parallel.

2. An electrical coil as defined in claim 1 and adapted for heavy duty usage and wherein said second layer comprises a plurality of uninsulated strips of material.

3. An electrical coil construction including a multilayer flexible strip conductor wound in turn layer form, said conductor comprising a first layer consisting of a single aluminum strip having first and second sides and rounded edges, and a second metallic layer having uninsulated first and second sides and with a thickness greater than and width less than that of said first layer, said layers being substantially coterminous and being arranged in side-by-side contact with each other, each of said layers being physically separate from each other and readily bendable around a forming mandrel, said first layer having an aluminum oxide insulation covering said first side and the edges thereof and establishing an insulating relation with respect to the second side of said second layer in the next succeeding turn of said coil and being uninsulated on at least a portion of the second side thereof for uninsulated contact with the first side of said second layer, and terminals for said coil attached to at least one of said layers at the ends thereof and serving to connect said layers in parallel.

References Cited in the file of this patent UNITED STATES PATENTS 1,331,077

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION A Patent No. 2 ,949, 593 I August 16, 1960 John Staley et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1 line 40, for "Serial No. 487 ,457" read Serial No. 487,057

Signed and sealed this 3rd day of January 1967.

Afloat:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Cner of Patents UNITED STATES :PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,949,593 August 16, 1960 John Staley et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 40, for "Serial No. 487,457" read Serial No. 487,057

Signed and sealed this 3rd day of January 1967.

' Afloat:

mN-EsT w. SWHJER EDWARD J. BRENNER Meeting 0m 'ncr of Fame 

